- Moving the implementations of class Inet4 and class Inet6 into separate
  files sql_type_inet.h and sql_type_inet.cc, in order to reuse them
  for the INET6 data type and inet function collection.
- Adding a warning in the case when IS_IPV4_MAPPED() and IS_IPV4_COMPAT()
  erroneously gets an IPv4 address instead of the expected IPv6 address.